Shrink tunnel for palletized loads

ABSTRACT

A shrink tunnel for shrinking a covering of plastic material onto a palletized load including apparatus for generating a curtain of air at entrance and exit of the tunnel to isolate a shrink zone within the tunnel from an ambient environment and to provide preheating and cooling of the plastic cover at entrance and exit, respectively, as the load moves through the tunnel. The shrink zone has a pair of stationary nozzles near the entrance of the tunnel for directing heated air at the skirt of the plastic covering adjacent the base of the palletized load to shrink the skirt to the pallet. The remainder of the covering is thereafter shrunk onto the load thereby protecting the load from the elements during shipment or storage and binding it to the pallet for convenient shipment.

[451 Apr. 17, 1973 3,404,508 10/1968Dreyfus............................. 3,522,688 8/1970 Ka1iw0da........

[ SHRINK TUNNEL FOR PALLETIZED LOADS [75] Inventor:

Hans Melgaard Mound Primary Examiner-Kenneth W. Sprague DespatchIndustries, Assistant Examiner-James C. Yeung neapolis, Minn.

Inc., Min- Assignee:

Attorney-Williamson, Palmatier & Bains, H. Dale Palmatier,'Herman H.Bains and Malcolm L. Moore 22 Filed: Sept. 18, 1970 [21] Appl. No.:73,393

[57] ABSTRACT A shrink tunnel for shrinking a covering of plasticmaterial onto a palletized load including apparatus for [52] US. Cl...........................34/2l6, 34/66, 34/225,

generating a curtain of air at entrance and exit of the tunnel toisolate a shrink zone within the tunnel from an ambient environment andto provide preheating and cooling of the plastic cover at entrance andexit, respectively, as the load moves through the tunnel.

0 3 0%3 w l b5 3 0 .3 0 WB "3 W 2 mm9 mm6 mm2 mmM 8 e S LM d Ld mm 1111100 55 [It [56] a References cued The shrink zone has a pair ofstationary nozzles near UNITED STATES PATENTS the entrance of the tunnelfor directing heated airat the skirt of the plastic covering adjacentthe base of the palletized load to shrink the skirt to the pallet. The

remainder of the covering is thereafter shrunk onto "219/333 the loadthereby protecting the load from the elements ...34/2l6 during shipmentor storage and binding it to the pallet 3 /216 UX for convenientshipment.

.34/216 9 Claims, 5 Drawing Figures Payton et al. 5/1964 Hagen et a1.

l SHRINK TUNNEL FOR PALLETIZED LOADS BACKGROUND OF THE INVENTIONTraditionally loads have been bound to pallets by metal straps or cords.Such retainers are adequate to hold the load on the pallet but providelittle protection from adverse weather and rough handling during transitor storage. Accordingly, it is desired to provide an apparatus whichrapidly binds the load securely to the pallet and provides protectionfor the load from weather and handling at a minimum of cost.

The present invention comprises a shrink tunnel for palletized loads. Aloaded pallet is covered with a wrapper of shrinkable or orientedplastic material and conveyed through the shrink tunnel to shrink thematerial into a tight fitting relationship with the load and palletthereby protecting the load and binding it to the pallet.

It is desirable to provide a preheating zone at the shrink tunnelentrance to warm the plastic covering prior to its encountering the hightemperature shrink zone. The invention includes apparatus to generate acurtain of preheating air at the tunnel entrance which simultaneouslypreheats the plastic and isolates the shrink zone from the ambientenvironment. Additional apparatus can be used to generate a curtain ofair at the exit of the tunnel to establish a cooling zone to decreasethe temperature of the plastic covering as the load leaves the tunneland further isolate the shrink zone from the ambient environment.

' Before the plastic cover is fully shrunk onto the palletized load, theplastic covering should be shrunk tightly against the pallet itself. Ifthis step is not taken, the plastic covering as a whole shrinks and theskirt of the covering recedes to a level above the pallet making itdifficult to thereafter anchor the load to the pallet with the plasticcovering. Accordingly, the invention includes apparatus to shrink theplastic covering against the sides of the pallet before shrinking theplastic covering against the load.

SUMMARY OF THEINVENTION The invention comprises a shrink tunnelforpalletized loads which shrinks a plastic covering against thepalletized load to provideprotection for the load and bind it to thepallet. A loaded pallet with a plastic covering thereover moves along aconveyor through the shrink tun'nel which includes a high temperaturenozzles near the entrance of the tunnel to shrink the plastic materialtightly against the sides of the pallet before the remainder of theplastic material is shrunk tightly against the load. The anchors theplastic materi al solidly to the pallet and when the final shrinking ofthe plastic covering occurs thereafter, the load is securely bound tothe pallet. The plastic covering provides protection against roughhandling and adverse weather.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictoral view of theshrink tunnel inven* tion with the outer tunnel wall partially cut away.

FIG. 2 is an enlarged sectional view taken along cutting plane 22 ofFIG. 1 showing the conveyor system used with the invention.

FIG. 3 is a section side view of the shrink tunnel of FIG. 1 with apalletized load entering the tunnel.

FIG. 4 is an enlarged sectional view of a preheating nozzle taken alongcutting plane 44 of FIG. 1.

FIG. 5 is an enlarged cross sectional view taken along cutting plane 5-5of FIG. 3 showing a stationary shrink nozzle.

DESCRIPTION AND OPERATION THE INVENTION FIG. 1 shows a palletized load10 about to enter a shrink tunnel shown generally at 12. The palletizedload 10, consisting of pallet 14 and load I6, has a bag-.

covering selected should be sturdy enough to provide protection to theload; polyethylene plastic with a thickness of approximately 5/1000 inchis acceptable.

The palletized load 10 with its wrapper 18 is moved along a conveyorsystem 24 which defines a path through the shrink tunnel. Referring nowto'FIGS. 1

shrink zone. The tunnel has apparatus for generating a curtain of air atentrance and exit to respectively preheat and.cool the plastic coveringas the palletized load passes therethrough. In addition the curtain ofair acts asan air door to isolate the shrink zone from the ambientenvironment. y

The shrink zone has apparatus for heating and circulating air at atemperature adequate to shrink the plastic material into tight fittingrelationship with the load. The apparatus includes a pair of stationaryshrink and 2 the conveyor has a pair of identical tracks 26 and 28 withroller chain drives 32 and 34. Moving roller chains 32 and 34 have aplurality of cross bars such as 36 attached transversely to the chainsat spaced intervals. The cross bars 36 engage the palletized load 10 tocarry it along tracks 26 and 28.

Referring now to FIG. 1, the shrink tunnel 12 has a tunnel housing 40which includes entrance 42 and exit 44. Approximatelyintermediate-between entrance and exit is an apparatus for establishinga shrink zone within the tunnel housing. The shrink zone apparatusincludes apparatus for heating and circulating air such as shrink zoneheater 46, shrink zone blower 48, ducts S0, 52, 58, and 59, shrinknozzles 60 and 62, shrinking arch 56 and shrink zone air return 54.Heater 46 warms air to a temperature range adequate to shrink theplastic wrapper l8, and blower 48 forces the shrinking air into ducts 50and'5 2 leading to shrinking arch 56 and into ducts 58 and 59terminating at stationary shrink nozzles 60-and 62. The arch 56 andshrink nozzles 60 and 62 release shrinking air to establish a shrinkingzone of sufficient volume to shrink the plastic wrapper 18 into asubstantially tight fitting relationship with the load. This temperaturerange varies with the physical and chemical properties of the plasticmaterial used, but for polyethylene with a thickness of S/lOOO inch, itis approximately 300400F.

It should be understood that the shown apparatus for heating andcirculating the air is but one means for raising the temperature of theshrink zone to a shrinking temperature range and that other means, suchas radiant heating, are contemplated as usable with the invention.

The shrink nozzles 60 and 62 are, of course, not the only apparatuswhich can be used to shrink the skirt of the wrapper against the sidesof the pallet. Any means for heating the plastic material adjacent thepallet to a shrinking temperature can be used to anchor the skirt to thepallet.

As the palletized load with a plastic wrapper thereover moves throughhousing 40 it encounters stationary shrink nozzles 60 and 62 beforereaching shrinking arch 56. Shrink nozzles 60 and 62 direct shrinkingair against the skirt 20 of the wrapper which overlies the sides of thepallet 14 and shrinks the skirt 20 tightly against the pallet to anchorthe wrapper thereto. Thus when palletized load reaches shrinking arch56, the wrapper is securely anchored to the pallet and as the air fromshrinking arch 56 beats the plastic wrapper, it shrinks into a tightfitting relationship with the load, binding it to the pallet.

The cross sectional configuration of a shrink nozzle 60 is shown in FIG.5. Lips 64 and 66 separated by slotted orifice 65 direct shrinking airoutward as shown by arrow 63', lip 64 being moveable to control thequantity of air released in order to adapt the shrink nozzle 60 toplastic materials having various thicknesses. A lesser quantity ofheated air is required to shrink a thin plastic covering than is neededfor a thicker covering. Nozzles 60 and 62 are elongated to extendlongitudinally along the conveyor 24 to provide continued heating of thewrapper shirk 20 to assure shrinkage of the wrapper against the pallet.

Most of the shrinking air expelled from shrinking arch 56 or shrinknozzles 60 and 62 circulates through the shrink zone and enters shrinkzone air return duct 54 which extends to the shrink zone heater 46 andblower 48 which repeatedly heat and circulate the air. Referring nowtoFIG. 3, the air return 54 is located below the level of a palletpassing through the shrink zoneQThis positioning creates a slight vacuumwithin the plastic wrapper 18 which minimizes billowing ofthe wrapper asit -passes through the tunnel. As will be further described hereafter aportion of the shrinking air from the shrink zone is accepted bypreheating zone air return 76 to aid in establishing preheating zone.

The tunnel entrance 42 is provided with apparatus for generating acombined air door and plastic wrapper preheating zone adjacent theentrance. The generating apparatus is shown in FIG. 1 as includingpreheating zone blower 70, outlet duct 72 exhaust duct 94, damper 92,preheating arch 74, preheating zone air return 76, and inlet duct 78.

Preheating zone air return 76 accepts both shrinking air from the shrinkzone and ambient air entering from the entrance 42 and combines them toobtain preheating air which has a temperature range lower than that ofthe shrinking air. This preheating air temperature range may be atapproximately 200250F for 5/1000 inch polyethylene plastic. Bymanipulating damper 92 in exhaust duct 94, a predetermined quantity ofair is exhausted from the shrink tunnel, thereby causing an essentiallyequal quantity of ambient air to enter through entrance 42 and exit 44.Preheating air is obtained by mixing the shrinking air with the ambientair. Blower delivers the preheating air to the preheating arch 74 whichincludes a plurality of interconnected preheating nozzles here shown asthe three nozzles 80, 82, and 84; naturally, a greater or lesser numberof nozzles can be used. Preheating nozzles and 84 have a lengthsubstantially equal to the height dimension of the entrance; nozzle 82has a length substantially equal to the width of the entrance dimension.FIG. 4 shows the cross sectional configuration of preheating nozzle 82mounted adjacent wall 85 of the tunnel housing. Each preheating nozzlehas a longitudinally disposed slotted orifice 87 extending substantiallythe length of the nozzle, and lips 88 and 90 adjoining the slottedorifice and separated thereby to direct preheating air across and intothe tunnel entrance 42.

Referring again to FIG. 4, the position of lip 90 of nozzle 82 can bevaried to control the volume of air expelled from the orifice in orderto balance the air flows from nozzles 80, 82, and 84 and generate thecurtain of preheating air. Operation of nozzles 80 and 84 is identicalto that of nozzle 82. The three preheating nozzles co-operate togenerate a curtain of air at the entrance 42 which establishes apreheating zone extending to return 76.

The flow pattern of the air issuing from preheating arch 74 is indicatedby flow arrows in FIGS. 1 and 3. The air flow of preheating nozzles 80and 84 is directed acrossand into the tunnel entrance; the air flow ofnozzle 82 is directed downward and into the entrance. As a load passesthrough the arch 74 the air from the arch flows along the load and intothe return 76 as shown in FIG. 3. Preheating air emitted from preheatingarch 74 heats the plastic covering as the load passes through the archand isolates the shrink zone from the ambient environment outside theentrance 42.

Most air expelled from preheating nozzles 80, 82, and 84 enters tunnelhousing 40 and is drawn into preheating zone air return 76 and conveyedby duct 78 to v the blower 70. Thus preheating air is circulated andrecirculated to generate a curtain of preheating air at the entrance ofthe tunnel housing.

Referring again to FIG. 1, exit 44 has a cooling zone generated bycooling arch 96 formed from a plurality of cooling nozzles, here shownas three interconnected nozzles identical to preheating nozzles 80, 82,and 84 of preheating arch 74. The cooling arch 96 receives its airsupply through duct 97 extending from cooling zone blower 98. A coolingzone air return 99 accepts air emitted from the cooling arch 96 andreturns it to the blower 98 for recycling. Thus the cooling arch 96 withits blower 98 generates a curtain of air at the exit which establishes acooling zone for the plastic wrapper and an air door which isolates theshrink zone from the ambient environment outside the exit. A damper 100exhausts a predetermined amount of air out duct 101 in order to causeambient air to enter the exit at a predetermined rate. Themixing'ofshrink zone air and ambient air'permits one to'obtain a supplyof cooling ture range as preheating air.

Although the apparatus forming the cooling zoneis i not shown asidentical to that for generating the pre heating zone, it should beunderstood that the same identical structure could have been used.

. In operation, a palletized load with a plastic covering 18 thereoveris placed on conveyor System24 which carries it through the shrinktunnel 12. The palletized load enters preheating arch 74 and preheatingair emitted from nozzles 80,82, and 8 4 preheats the plasticcovering18.As the load passes through entrance 42 the preheating air flows aboutits periphery,

rapidly warming the plastic in'preparation for its entering theshrink'zone The nozzles 80, 82 and 84 establish 'a curtain of air whichisolates the shrink zone from the ambient environment. Most air frompreheating arch 74 is picked up by air return 76 by recycled.

As the plastic covering encounters stationary shrink nozzles 60 and 62which as shown in HO. 1 are disposed in the preheating zone to shrinkthe skirt onto the pallet while preheating-Pair continues to be appliedto upper portions of the cover, shrinking air shrinks the skirt 2 0 ofthe plastic cover into a tight fitting relationship with the pallet.This anchors the skirt to the pallet and prevents the plastic coveringfrom shrinking upward and uncovering the lower sides of theload inresponse to heat from the still to be encountered shrinking arch 56. Theremainder of the plastic covering is shrunk into tight fittingrelationship a with. the load as the palletized load moves past theshrinking arch 56. It should be understood that the shrinking arch 56 isnot part of the invention and can be replaced by any known equivalentstructure.

As p alletized loadv l0 leaves the shrink zone and passes through exit44 the plastic covering is cooled by air emitted from cooling arch 96which functions identically to preheating arch 74. The cooling arch 96reduces the temperature of the plastic wrapper 18 permitting earlierhandling thereof, and also isolates the shrink zone from the ambientenvironment.

While I have described a preferred embodiment of a the presentinvention, it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

What is claimed is: t

l. A shrink tunnel to shrink a plastic wrapper covering a palletizedload into a substantially tight fitting relationship with the palletizedload as the load moves along a path through the tunnel comprising:

apparatus for generating a combined air door andplasticwrapperpreheating zone adjacent the housing entrance, said generating apparatusaccepting heatedair from the shrink zone and unheatedambient air andcombining them. to obtain preheating air having a temperature range lessthan that required to shrink the plastiewrapper, said preheating airbeing, conveyed to the entrance to generate a curtain of air directedacross and into 7 the entrance to thereby preheat a plastic wrapperentering the tunnel housing and isolate the shrink zone from an ambientenvironment.

2. The combination according to claim 1 wherein said means for raisingthe temperature in the shrink zone includes:

apparatus for heating and circulating air, the apparatus heating the airto apredetermined temperature range adequate to shrink the plasticwrapper onto the palletized load and circulating the shrinking airthrough the housing to establish a shrink zone at a distance from theentrance thereof containing an adequate volume of shrinking air toshrink the plasticwrapper into a substantially tight fittingrelationship with the palletized load. 3. The combination according toclaim 1 wherein the apparatus for generating a combined air door andplastic wrapper preheating zone further includes:

a preheating zone blower; 3 i

a preheating zone air return conveying said preheating air from thetunnel housing to said preheating zone blower;

a plurality of preheating nozzles receiving said preheating air fromsaid preheating zone blower and located aboutthe entrance for emissionof said preheating air to generate the curtain of air.

4. The combination according to claim 3 wherein an outlet duct extendingfrom the preheating zoneblower to the said nozzles supplies air to thenozzles, said outlet duct having a damper therein adjacent the preheating zone blower to exhaustair from the tunnel-housing thereby causingambientair to enter thehousing at'a predetermined rate therebycontrolling the temperature of said preheating air. e v

5. The combination according to claim 3 wherein each preheating nozzlehas a longitudinally disposed slotted orifice and a pair of lipsadjoining the slotted orifice and separatedthereby to directpreheatingair issuing therefrom across and into the tunnel entrance togenerate the curtain of air.

6. The combination according to. claim 5 wherein one of the lips of eachpreheating nozzle is moveable relative to the slotted orifice tocontrollably obstruct air passing about the exit to expel the'airtherefrom thereby generating a curtain of air adjacent the exit.

8. A tunnel to shrink a plastic cover on a palletized load into atightfitting relationship with the load comprising:

a tunnel housing including an entrance and exit;

a conveyor moving the palletized load through the housing;

means heating and circulating shrinking air inside the housing toestablish a shrink zone in spaced relation to the entrance, thetemperature of the shrinking air being adequate to shrink the cover intotight fitting relationship with the palletized load as the load movesthrough the shrink zone;

second means for supplying an independent preheating zone of airimmediately adjacent the entrance and having a temperature substantiallyless than the shrinking zone air;

said heating and circulating means also including a pair of stationaryshrink nozzles between the preheating zone and the shrink zone, onenozzle being located on each side of said conveyor adjacent the conveyorand on a vertical level with a pallet moving therealong, the nozzlesdirecting shrinking air substantially horizontally across the housingand at the sides of the pallet as the load passes through the preheatingzone to thereby shrink the'skirt of the cover to tightly grip the palletprior to the load entering the shrink zone wherein the remainder of thecover is shrunk onto the load.

9. The combination according to claim 8 wherein said second meansincludes a plurality of entrance nozzles arranged to direct preheatingair against the top and sides of the palletized load, said second meansfurther including an air return spaced along the tunnel housing from theentrance nozzles so the preheating air flows along and preheats the topand sides of the palletized load, and then enters the air return, thepreheating zone extending along the tunnel housing to said air return,the shrink nozzles being disposed in the portion of the tunnel housingcontaining the preheating zone to g the cover.

1. A shrink tunnel to shrink a plastic wrapper covering a palletizedload into a substantially tight fitting relationship with the palletizedload as the load moves along a path through the tunnel comprising: atunnel housing including an entrance and exit; apparatus forestablishing a shrink zone within the tunnel housing, the apparatusincluding means for raising the temperature of the shrink zone to atemperature range adequate to shrink the plastic wrapper into asubstantially tight fitting relationship with the palletized load as theload moves along the path through the shrink zone; apparatus forgenerating a combined air door and plastic wrapper preheating zoneadjacent the housing entrance, said generating apparatus acceptingheated air from the shrink zone and unheated ambient air and combiningthem to obtain preheating air having a temperature range less than thatrequired to shrink the plastic wrapper, said preheating air beingconveyed to the entrance to generate a curtain of air directed acrossand into the entrance to thereby preheat a plastic wrapper entering thetunnel housing and isolate the shrink zone from an ambient environment.2. The combination according to claim 1 wherein said means for raisingthe temperature in the shrink zone includes: apparatus for heating andcirculating air, the apparatus heating the air to a predeterminedtemperature range adequate to shrink the plastic wrapper onto thepalletized load and circulating the shrinking air through the housing toestablish a shrink zone at a distance from the entrance thereofcontaining an adequate volume of shrinking air to shrink the plasticwrapper into a substantially tight fitting relationship with thepalletized load.
 3. The combination according to claim 1 wherein theapparatus for generating a combined air door and plastic wrapperpreheating zone further includes: a preheating zone blower; a preheatingzone air return conveying said preheating air from the tunnel housing tosaid preheating zone blower; a plurality of preheating nozzles receivingsaid preheating air from said preheating zone blower and located aboutthe entrance for emission of said preheating air to generate the curtainof air.
 4. The combination according to claim 3 wherein an outlet ductextending from the preheating zone blower to the said nozzles suppliesair to the nozzles, said outlet duct having a damper therein adjacentthe preheatIng zone blower to exhaust air from the tunnel housingthereby causing ambient air to enter the housing at a predetermined ratethereby controlling the temperature of said preheating air.
 5. Thecombination according to claim 3 wherein each preheating nozzle has alongitudinally disposed slotted orifice and a pair of lips adjoining theslotted orifice and separated thereby to direct preheating air issuingtherefrom across and into the tunnel entrance to generate the curtain ofair.
 6. The combination according to claim 5 wherein one of the lips ofeach preheating nozzle is moveable relative to the slotted orifice tocontrollably obstruct the orifice and thereby vary the volume of airpassing through the orifice.
 7. The combination according to claim 1including: a cooling zone blower; a cooling zone air return located inthe tunnel housing between the shrink zone and the exit conveying airfrom within the tunnel housing to the cooling zone blower; and aplurality of cooling nozzles receiving the air from said cooling zoneblower, the nozzles located about the exit to expel the air therefromthereby generating a curtain of air adjacent the exit.
 8. A tunnel toshrink a plastic cover on a palletized load into a tight fittingrelationship with the load comprising: a tunnel housing including anentrance and exit; a conveyor moving the palletized load through thehousing; means heating and circulating shrinking air inside the housingto establish a shrink zone in spaced relation to the entrance, thetemperature of the shrinking air being adequate to shrink the cover intotight fitting relationship with the palletized load as the load movesthrough the shrink zone; second means for supplying an independentpreheating zone of air immediately adjacent the entrance and having atemperature substantially less than the shrinking zone air; said heatingand circulating means also including a pair of stationary shrink nozzlesbetween the preheating zone and the shrink zone, one nozzle beinglocated on each side of said conveyor adjacent the conveyor and on avertical level with a pallet moving therealong, the nozzles directingshrinking air substantially horizontally across the housing and at thesides of the pallet as the load passes through the preheating zone tothereby shrink the skirt of the cover to tightly grip the pallet priorto the load entering the shrink zone wherein the remainder of the coveris shrunk onto the load.
 9. The combination according to claim 8 whereinsaid second means includes a plurality of entrance nozzles arranged todirect preheating air against the top and sides of the palletized load,said second means further including an air return spaced along thetunnel housing from the entrance nozzles so the preheating air flowsalong and preheats the top and sides of the palletized load, and thenenters the air return, the preheating zone extending along the tunnelhousing to said air return, the shrink nozzles being disposed in theportion of the tunnel housing containing the preheating zone to shrinkthe skirt of the cover onto the pallet while preheating air continues tobe applied to upper portions of the cover.